The invention relates to a method for operating intrinsically safe battery cells after charging of an intrinsically safe battery cell at a low temperature.
Battery cells are used in numerous ways in energy storage systems for stationary as well as mobile applications, such as, for example, in emergency power systems or in the automotive industry for electric and hybrid vehicles. In these applications, a plurality of battery cells are connected to one another in series and/or also in parallel to form battery modules and batteries.
Due to manufacturing tolerances and or age related losses of capacity, the capacity of the battery cells connected together to form batteries is not always exactly the same. Charging and discharging of the battery cells, however, typically occurs jointly in a composite, whereby there is, for example, the danger of overcharging or deep discharging individual battery cells. There is consequently the danger of overheating individual battery cells, which generally leads in multiple steps to a thermal destruction of the corresponding battery cell.
For this reason, there is a need to provide intrinsically safe battery cells which comprise safety components for the protection thereof. These include inter alia functions and devices such as safety switches CID (current interrupt device), valves for pressure relief or thermal protection devices against overheating due to overcharging or excessive current flow. In a simple case, an intrinsically safe battery comprises a switching device, with the help of which the intrinsically safe battery cell can be deactivated within the battery while the remaining battery cells of the battery can be further operated.
Intrinsically safe battery cells, such as intrinsically safe lithium ion cells, comprise in accordance with the prior art electronic components, such as, for example, a rapid discharging device in order to protect the battery cell in situations such as an internal or external short circuit, overcharging, deep discharging or external overheating.
Mechanisms that lead to an internal short circuit of a battery cell include plating. In this case, positively charged ions are not introduced into the structure of the electrode during the charging procedure but are deposited as a layer on said electrode. The layers of the deposits can lead to a short circuit between the electrodes. This effect can particularly occur when charging with very high currents or at low temperatures. Temperatures of approximately 0° Celsius and below are regarded here as low temperatures.
In this context, a rechargeable lithium cell comprising a reference electrode for monitoring the state of health thereof is know from the WIPO patent application WO 2009/036444 A2. The lithium cell comprises a battery management system including a state of charge monitor in order to obtain information in regard to a potential difference between the operating electrodes and the potential at one or a plurality of operating electrodes with respect to a reference electrode.
Furthermore, a battery control module is known from the U.S. Pat. No. 7,982,437 B2, which monitors discharge voltages that are associated with a traction battery of a vehicle. The battery control module operates the traction battery cyclically with a charging voltage-dependent charging/discharging profile in order to generate heat in the traction battery. If the temperature of the traction battery lies below a limit value, for example 10° C., the battery control module will operate the traction battery cyclically in order, for example, to generate heat during an early range of the vehicle operation at cold temperature conditions.